Make caramel: Pour 200 grams (1 cup) sugar and the 10 grams of water into a saucepan, preferably one that is white or light-colored inside. Place over medium heat and bring to a boil, swirling the pan to combine the sugar and water. Do not stir.

Let boil until deep amber in color, swirling the pan occasionally to caramelize evenly, about 10 minutes total. Watch the pan carefully after the mixture starts turning golden; it will quickly become light brown, then amber, then dark amber. Immediately pour caramel into a 9- by -5-inch loaf pan and swirl to coat the bottom and sides evenly. Set aside to harden.

In a blender (or using a hand blender in a pitcher), combine eggs, egg yolks and vanilla. Blend until smooth.

Remove the lemon zest strips from the hot milk mixture. With the blender running, gradually pour the milk mixture into the eggs. Go very slowly at first so that the eggs don’t cook from the heat of the milk. Blend just until smooth. Pour egg-milk mixture through a fine colander into the caramel-lined pan.

Place a 9- by- 13-inch baking dish in the lower third of oven. Carefully place the loaf pan in the baking dish. Pour hot tap water into the baking dish until it comes about halfway up the sides of the loaf pan. (Don’t worry if the oven seems to be losing heat; the flan will adjust.)

To unmold, run a thin sharp knife around the edges and rest the bottom of the pan on a hot wet kitchen towel for a few minutes. Center a flat-bottomed platter or serving dish with a rim on top of the pan and, holding both, carefully flip the pan and plate together. The flan will fall onto the plate with a squelch; lift off the pan and let the caramel run all over the top.